1. Field of Invention
The present invention relates to a signal communication system, more particularly to a cable television optical fiber communication system and optical signal transmission device thereof.
2. Description of Related Art
For a conventional Optical Cable Television System, operations of signal download/upload of plural set-top boxes (STBs) provided at user ends all communicate via a same optical fiber. That is, when a signal download operation for a user end is processed, image signals are downloaded from a center office (i.e. provider end) to the user end via an optical fiber, and when an upload operation for the user end is processed, the user end uploads analog signals to the center office via the same optical fiber. Another communication operation of a user end is that a return operation is individually designed so only uploading information is returned to a center office (i.e. provider end), one end thereof is connected to a getway of a FTTH (Fiber To The Home) via an optical fiber for receiving cable television signals received by the getway; the other end is connected to a user end for transferring television channel signals to the user end, upload information of the user end is returned to a light emitting end of the module for returning back to the center office.
The FTTH module is a method of optical fiber communication, an active optical network or a passive optical network can be adopted for information communication. Equipments of a center office of the passive optical network are provided on an optical line terminal (OLT). Optical signals downloaded from the optical line terminal are distributed to plural optical network units (ONU) by an optical wave distribution unit of an optical splitter via an optical fiber for providing a broad-band communication capacity of single end to plural ends.
When plural optical network units of user ends are simultaneously connected to one center office, regardless that whether the optical network units return signals back to the center office, each of the optical network units constantly emits lasers to the center office; because a receiving device of the center office is not able to simultaneously receive plural lasers emitted by the user ends, optical communication would be overloaded and not able to normally receive the lasers, work efficiency is therefore lowered. So how to provide a sufficient solution for improving the described disadvantage and also meet customers' needs and raise the competitiveness in the market place shall be seriously concerned.